The congestion window is a number that directs the size of the sliding window to

Question

The congestion window is a number that directs the size of the sliding window to be used. TCP keeps track of the congestion window w at a host by constantly updating it, and the precise rules are as follows: 1) Every time a positive acknowledgment comes in, w w + 1/w , and 2) every time a lost packet is detected, w w/2 . Let p be the probability that a packet is lost.

1.What is the expected change of the congestion window?

2.Given p, what congestion window will keep the expected change above equal to 0?

Explanation / Answer

1.

We use the simple formula for this:

square root of [{2(1-p)}/p]

where p is the probability that a packet is lost.

2.

let this expected change be cwp

so cwp = square root of [{2(1-p)}/p]

now for cwp>=0,

we have

square root of [{2(1-p)}/p] >=0

Now squaring both sides

[{2(1-p)}/p] > = 0

solving this we get p<=2

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